Due to its high acid content, I would think it's perfectly fine to can curd the same way that you can jam—with a hot water bath. You can find lots of instructions for this method online. Maybe also get confirmation from a trustworthy source that it's safe to can curd, just to be safe...

The Nigella Lawson recipe says to keep it in the refrigerator, and since it includes eggs, I'd think it's not quite as safe and easy as canning jams.

The info I've seen on canning lemon curd does say that it's okay in a water bath, no need for pressure canning, but keep the jars small, and don't anticipate a long shelf life. Look for color changes or separation, and plan to eat it up in a couple of months.

But passionfruit? I'm not sure. Here's a link to a University of Georgia publication on lemon and lime curd. http://www.uga.edu/nchfp...